L-Mannose → (2R,3S,4S,5R)-2,3,4,5,6-pentahydroxyhexanal

It is also known that both D-glucose and D-mannose can be epimerized in an aqueous solution containing about 17% by weight of D-glucose or D-mannose, based on total solution weight (i.e., 20% by weight of glucose, based on the weight of water) and a small amount of molybdic acid catalyst producing a solution containing 25 percent D-mannose, remainder D-glucose on the dry basis. This epimerization is described by V. Bilik, Chem. Zvesti, 26, 183-186 (1972) and in Czech patent 149,051 (June 15, 1973). No reaction took place when sodium molybdate was used as the catalyst. Bilik and co-workers have also found that various other sugars can be epimerized in the presence of molybdate ions in aqueous solution. For example, D-fructose gives a mixture of D-sorbose, D-tagatose, and D-psicose, and sucrose gives a mixture of D-mannose and D-sorbose in a similar reaction. [Chemical Abstracts, 80, 146433s (1974)]. Also, L-arabinose gives a mixture of L-arabinose and L-ribose [Czechoslovakian Patent 149,472, July 15, 1973; C.A. 81, 78189k (1974)]; L-mannose gives a mixture of L-glucose and L-mannose [C.A. 81, 91887f (1974)]; and D-galactose gives a mixture of D-talose and D-gulose in addition to D-galactose [C.A. 81, 152523h (1974)].